Assuming you are using windows, your saves are stored in C:\Users\[generic_username,_insert_yours_here]\AppData\Roaming\Factorio\saves
You can email it to your friend (or you can send it through Steam if Steam allows sending files) and you friend (again, assuming they are using windows) can put it in C:\Users\[generic_username,_insert_your_friend's_here]\AppData\Roaming\Factorio\saves
Factorio should notice the save and your friend can play it all they'd like.

There are 10 types of people: those who get this joke and those who don't.